The presence of a ventral component of globus pallidus in the olfactory tubercle was suggested by histochemical, hodological, and electron microscopic evidence. The presence of certain molecular makers, especially iron, in the more dorsal neo-pallidum led to the hypothesis that the purported ventral pallidum in the olfactory tubercle should exhibit the same features. Refinements in the Perl's method for detecting ferric-iron allowed iron to be visualized in all the areas of rat brain previously reported for human brain. The iron-positive zone of the ventral pallidum was seen to extend into the olfactory tubercle of rat, hamster, squirrel monkey, and opossum. These observations together with the reports of high levels of other pallidal molecular markers, the neurotransmitter GABA, and its synthesizing enzyme glutamic acid decarboxylase, provide a strong argument for the presence of a pallidal component in the olfactory tubercle. Phylogenetically, this component may be the primordial or paleo-pallidum.